1. Field of the Invention
The present invention relates to an ink film tension device for applying a tension to an ink film in a cartridge used in a color video printer, and more particularly to an ink film tension device for applying a reverse rotation force to a supply reel of the cartridge, so as to apply a tension to the ink film.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a general color video printer. As shown in FIG. 1, the color video printer comprises a printer body 1 and a cartridge receiving guide 2 disposed in the interior of printer body 1. A holder 5 is pivotally mounted to the printer body 1 to pivot about a pivot pin 6 and disposed above the cartridge receiving guide 2. The holder 5 carries a thermal print head 3 and a thermal print head sensor 4. Beneath the cartridge receiving guide 2, a pinch roller 7 and a grip roller 8 are disposed which are in press contact with each other at a certain pressure. Near the rollers 7 and 7 is disposed a platen roller 9.
In the cartridge receiving guide 2, a cartridge 10 is received which includes a rotatable supply reel 11 and a rotatable take-up reel 12 spaced from the supply reel 11, as shown in FIGS. 2A and 2B. An ink film 13 is wound around the supply reel 11 and the take-up reel 12. The cartridge 10 also has a rectangular opening at its bottom portion.
The ink film 13 has three color portions, that is, a yellow portion 15, a cyan portion 16 and a magenta portion (not shown). As shown in FIG. 2A, a transparent portion 17 is provided between the yellow portion 15 and the cyan portion 16, at the initial operation portion of the ink film 13.
The color video printer with the above-mentioned construction operates under the condition that the cartridge 10 is loaded in the cartridge receiving guide 2. As the holder 5 pivots in a counter-clockwise direction about the pivot pin 6 under the condition that a copy sheet 18 has been fed between the pinch roller 7 and the grip roller 8, the thermal print head sensor 4 senses the transparent portion 17 formed between the yellow portion 15 and the cyan portion 16 of the ink film 13 and sets the standby position of the ink film for initiating a printing from the yellow portion 15.
At this time, the ink film 13 which has been at a position A in FIG. 1 is lowered to be at a position A' in FIG. 1 so that it comes into contact with the copy sheet 18 being fed according to the rotation of pinch roller 7, so as to achieve a printing.
After the printing; the holder 5 pivots in a clockwise direction about the pivot pin 6 and returns to its original position. Simultaneously, the ink film 13 returns from the position A' to the position A. However, the returning operation of ink film 13 may not be assuredly carried out. In this case, the ink film 13 may be released, thereby causing it to get caught in the cartridge receiving guide 2 and thereby tear and damage. As a result, it is difficult to obtain a good quality of pictures.
An ink film tension device for avoiding such a phenomenon has been known which applies a tension to the ink film by rotating reversely the supply reel of cartridge through a certain angle after the holder returns. A typical example of such an ink film tension device is illustrated in FIGS. 3 and 4.
As shown in FIGS. 3 and 4, the ink film tension device comprises a fixed shaft 22 fixedly mounted to a reel bracket 21, a resilience member 23 disposed around the fixed shaft 22, and a reel hub 25 rotatably mounted to the fixed shaft 22 and surrounding the resilience member 23. The reel hub 25 has a gear portion 24 at its peripheral surface. A reel body 27 is also rotatably mounted to the fixed shaft 22 to rotate integrally with the reel hub 25 by means of a felt member 26 interposed between the reel hub 25 and the reel body 27. With the gear portion 24 of the reel hub 25 is engaged a worm gear 28 which is also engaged with a worm 30 of a motor 29.
In the ink film tension device with the above-mentioned construction, the motor 29 is actuated, just after the holder 5 returns to its original position. As the motor 29 drives, its drive force is transmitted through the worm 30, the worm gear 28, the gear portion 24 of reel hub 25, the felt 26, to the reel body 27 so that a hub 31 of the cartridge 10 engaged with the reel body 27 rotates through a certain angle, thereby causing the ink film 13 to be reversely fed. Accordingly, the ink film 13 is maintained at a tensed state.
However, this conventional ink film tension device requires the use of an additional motor such as the motor 29 and has a complicated construction, resulting in an increase in manufacture cost and a decrease in productivity.